(1) Field of the Invention
This invention relates to a seat belt system for a vehicle, and more particularly to a mechanism for adjusting the relative angle between a base plate (i.e., a slider) and an anchor plate in the seat belt system.
(2) Description of the Related Art
Passive seat belt systems for automobiles are known in which, after an occupant has seated, a webbing is automatically applied to the occupant. Usually, a guide rail is mounted on an inner wall of an automobile body and a travelling member (slider) carrying the webbing extending therethrough is caused to run on and along the rail to restrain or release the occupant.
In an alternative form, a base plate is attached to a center-pillar-side upper portion of a door, and the webbing is connected to the base plate via an anchor plate. When the door is closed, the webbing restrains the body of an occupant.
Practically, a seat belt system should be useful for occupants of different sizes. So in order to secure the safety for any occupant, it is necessary to adjust the height and angle of a shoulder part of the seat belt system. For this purpose, the known seat belt system is equipped with a mechanism for adjusting the position of a shoulder anchor.
To this end, the adjusting mechanism includes an anchor, to which the webbing is connected, and a base plate (slider) fixed to the automobile body or the door. For adjusting the relative angle between the anchor plate and the base plate (slider) to a most suitable angle depending on the body size of an occupant and the position of a seat while the occupant assumes a restrained position, a pin having a circular cross section is employed at the joint between the base plate (slider) and the anchor plate and serves as a pivot about which the anchor plate is angularly movable.
FIG. 22 shows a prior art adjusting mechanism of the type in which the anchor plate is angularly movable about a pivot pin. In the prior art adjusting mechanism, the extent of vertical adjustment is determined by the angle of rotation .theta. and the distance L from the center of rotation to a webbing attaching point. However, since the webbing attaching point located most preferably rearwardly of the automobile body, it is also preferable to reduce the distance L to a minimum. Consequently with this prior art mechanism, only inadequate effect can be achieved in vertical adjustment.
Yet, if it could be considered to achieve an adjustment by moving the anchor plate and the base plate vertically, the base plate (or the anchor plate) is necessarily large in the type in which the base plate is movable along a guide rail. This is contrary to the rule that a movable member should be preferably small in size. Therefore the prior art arrangement is not practical.